1. INTRODUCTION. 



IT is generally acknowledged that Leeuwenhoek was the first to 

 observe bacteria under the microscope, and his discovery of them was 

 made in the year 1675. In order to test the power of his lenses he 

 extracted from the human mouth what he regarded as promising 

 material, and subjected it to observation. In this material he found 

 small organisms which exhibited movement, and on this account, he 

 called them animalculae, the idea at that time being that power of 

 movement was confined to the animal kingdom. In 1683 his results, 

 accompanied by drawings, were communicated to the Royal Society, 

 which was then in its infancy. The forms which he described then 

 were the cylindrical, spiral, and round kinds, which to-day are known, 

 respectively, as Bacillus, Spirillum, and Coccus. But the importance of 

 his discovery was not appreciated, even by Leeuwenhoek himself, and 

 we have to wait for more than a hundred years before we see any 

 further notice taken of these forms; then in 1786 appeared Miiller's 

 Animalcula infusoria, fluviatilia et terrestria. In this work also the 

 bacteria are placed in the animal kingdom, though the author 

 admits that they bear resemblances to some members of the 

 vegetable kingdom. It is evident, in perusing Miiller's researches, 

 that the names he uses refer to classes of organisms, rather than to 

 species. 



The next work of note is that published by Ehrenberg in 1838. 

 Although he still classified bacteria as organisms belonging to the 

 animal kingdom, his work has the distinctive merit of marking off 

 sharply the various genera. 



His publication concerns itself with an examination of the Infusoria, 

 which he divides into twenty-two families. Under one of these 



A 



